A switching roller finger follower is used to control a valve in a valve train for an internal combustion engine. Arms for the follower are pivotably connected to a housing for the follower and positioned to enable contact with various lobes on a cam shaft. An element, such as a pin, in the follower is displaceable such that the element is either in a locked or an unlocked position with respect to the arms. In the locked position, respective ends of the element are aligned with respective arms such that when respective cam lobes contact the arms to pivot the arms, the arms engage the respective ends of the element. Since the engagement of the arms with the respective ends of the element locks the housing to the arms, the motion of the cam lobes is transferred to the housing to pivot the housing to operate (open and close) the valve. At the onset of the locked mode, when the respective ends of the element are aligned with the arms, but before the cam lobes begin to pivot the arms toward the elements, there is a gap, or lash, between the respective ends of the element and the arms. However, the dimensions of the respective ends of the element, such as the diameter, are subject to manufacturing and tolerance variations. Therefore, there is typically an unpredictable variation in the lash between the respective ends of the element and the outer arms for a single finger follower.
The same manufacturing and tolerance variations can causing varying amounts of unpredictable lash among finger followers in a production run of finger followers. The design of components for a cam shaft interfacing with the finger follower is impacted by the lash in the follower, for example, the design can optimize dimensions or configurations of components according to an expected lash. However, due to the unavoidable manufacturing and tolerance variations noted above, respective lash for individual followers in the production run cannot be predicted. As a result, the design of the components noted above must accommodate a larger range of possible lash dimensions, preventing optimization of the design.
Ideally, the lash for a finger follower would be as small as possible and would be identical for both ends of the element. However, due to the manufacturing and tolerance variations noted above, it is not possible to control the lash more tightly or predictably than within the range of the manufacturing and tolerance variations. That is, once the elements are installed, the lash variation is fixed and cannot be altered. Increased lash slows operation of the finger follower by requiring more time for the cam lobes to pivot the housing (operate the valve), since the amount of pivoting of the arm by the cam lobes to contact the elements and begin pivoting of the housing is increased. When the lash between the respective elements and arms is different, one cam lobe causes one of the arms to more quickly engage a respective end of the element than another cam lobe causes the other arm to engage the other end of the element, which can adversely affect operation of the finger follower.
In an unlocked mode, the respective ends of the element are misaligned with the arms, and the arms are free to pivot without contacting the elements. Thus, when the respective cam lobes on the cam shaft contact the outer arms, the arms pivot to accommodate the contact with the cam lobes and a position of the housing is not modified due to the contact between the cam lobes and the arms. In general, another cam contacts a different point, for example, the bearing, on the follower to displace the follower to operate the valve when the arms are in the unlocked mode.
To secure the element to the follower, retaining devices are affixed to ends of the element. In general, additional fabricating steps must be performed to provide features or profiles on the element to accommodate the retaining devices. For example, machined grooves are added to the ends to receive retaining rings. The extra fabricating steps and components add to the cost and complexity of the follower.